Network Working Group A. Fredette, Ed.
Request for Comments: 4209 Hatteras Networks
Category: Standards Track J. Lang, Ed.
Sonos Inc.
October 2005
Link Management Protocol (LMP) forDense Wavelength Division Multiplexing (DWDM) Optical Line Systems
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
The Link Management Protocol (LMP) is defined to manage traffic
engineering (TE) links. In its present form, LMP focuses on peer
nodes, i.e., nodes that peer in signaling and/or routing. This
document proposes extensions to LMP to allow it to be used between a
peer node and an adjacent optical line system (OLS). These
extensions are intended to satisfy the "Optical Link Interface
Requirements" described in a companion document.
1. Introduction
Networks are being developed with routers, switches, optical cross-
connects (OXCs), dense wavelength division multiplexing (DWDM)
optical line systems (OLSes), and add-drop multiplexors (ADMs) that
use a common control plane (e.g., Generalized MPLS (GMPLS)) to
dynamically provision resources and to provide network survivability
using protection and restoration techniques.
The Link Management Protocol (LMP) is being developed as part of the
GMPLS protocol suite to manage traffic engineering (TE) links
[RFC4204]. In its present form, LMP focuses on peer nodes, i.e.,
nodes that peer in signaling and/or routing (e.g., OXC-to-OXC, as
illustrated in Figure 1). In this document, extensions to LMP are
proposed to allow it to be used between a peer node and an adjacent
optical line system (OLS). These extensions are intended to satisfy
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RFC 4209 LMP for DWDM Optical Line Systems October 2005
In this model, a peer node may have LMP sessions with adjacent OLSes,
as well as adjacent peer nodes. In Figure 2, for example, the OXC1-
OXC2 LMP session can be used to build traffic-engineering (TE) links
for GMPLS signaling and routing, as described in [RFC4204]. The
OXC1-OLS1 and the OXC2-OLS2 LMP sessions are used to exchange
information about the configuration of the DWDM optical link and its
current state and information about the state of LSPs using that
link.
The latter type of LMP sessions is discussed in this document. It is
important to note that a peer node may have LMP sessions with one or
more OLSes and an OLS may have LMP sessions with one or more peer
nodes.
Although there are many similarities between an LMP session between
two peer nodes and an LMP session between a peer node and an OLS,
there are some differences as well. The former type of LMP session
is used to provide the basis for GMPLS signaling and routing. The
latter type of LMP session is used to augment knowledge about the
links between peer nodes.
A peer node maintains its peer node-to-OLS LMP sessions and its peer
node-to-peer node LMP sessions independently. This means that it
MUST be possible for LMP sessions to come up in any order. In
particular, it MUST be possible for a peer node-to-peer node LMP
session to come up in the absence of any peer node-to-OLS LMP
sessions, and vice versa.
1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
The reader is assumed to be familiar with the terminology in
[RFC4204].
DWDM: Dense wavelength division multiplexing
OLS: Optical line system
Opaque:
A device is called X-opaque if it examines or modifies the X
aspect of the signal while forwarding an incoming signal from
input to output.
OXC: Optical cross-connect
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RFC 4209 LMP for DWDM Optical Line Systems October 2005
Transparent:
As defined in [RFC4204], a device is called X-transparent if it
forwards incoming signals from input to output without examining
or modifying the X aspect of the signal. For example, a Frame
Relay switch is network-layer transparent; an all-optical switch
is electrically transparent.
1.2. Scope of LMP-WDM Protocol
This document focuses on extensions required for use with opaque
OLSes. In particular, this document is intended for use with OLSes
having SONET, SDH, and Ethernet user ports.
At the time of this writing, work is ongoing in the area of fully
transparent wavelength routing; however, it is premature to identify
the necessary information to be exchanged between a peer node and an
OLS in this context. Nevertheless, the protocol described in this
document provides the necessary framework in which to exchange
additional information that is deemed appropriate.
2. LMP Extensions for Optical Line Systems
LMP currently consists of four main procedures, of which the first
two are mandatory and the last two are optional:
1. Control channel management
2. Link property correlation
3. Link verification
4. Fault management
All four functions are supported in LMP-WDM.
2.1. Control Channel Management
As in [RFC4204], we do not specify the exact implementation of the
control channel; it could be, for example, a separate wavelength,
fiber, Ethernet link, an IP tunnel routed over a separate management
network, a multi-hop IP network, or the overhead bytes of a data
link.
The control channel management for a peer node-to-OLS link is the
same as for a peer node-to-peer node link, as described in [RFC4204].
To distinguish between a peer node-to-OLS LMP session and a peer
node-to-peer node LMP session, a new LMP-WDM CONFIG object is defined
(C-Type = 2). The format of the CONFIG object is as follows:
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RFC 4209 LMP for DWDM Optical Line Systems October 2005
Class = 6
o C-Type = 2, LMP-WDM_CONFIG
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|W|O| (Reserved) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Reserved field should be sent as zero and ignored on receipt.
WDM: 1 bit
This bit indicates support for the LMP-WDM extensions defined
in this document.
OLS: 1 bit
If set, this bit indicates that the sender is an optical line
system (OLS). If clear, this bit indicates that the sender is
a peer node.
The LMP-WDM extensions are designed for peer node-to-OLS LMP
sessions. The OLS bit allows a node to identify itself as an OLS or
a peer node. This is used to detect misconfiguration of a peer
node-to-OLS LMP session between two peer nodes or a peer node-to-peer
node LMP session between a peer node and an OLS.
If the node does not support the LMP-WDM extensions, it MUST reply to
the Config message with a ConfigNack message.
If a peer node that is configured to run LMP-WDM receives a Config
message with the OLS bit clear in LMP-WDM_CONFIG object, it MUST
reply to the Config message with a ConfigNack message.
2.2. Link Verification
The Test procedure used with OLSes is the same as described in
[RFC4204]. The VerifyTransportMechanism (included in the BeginVerify
and BeginVerifyAck messages) is used to allow nodes to negotiate a
link verification method and is essential for line systems that have
access to overhead bytes rather than the payload. The VerifyId
(provided by the remote node in the BeginVerifyAck message and used
in all subsequent Test messages) is used to differentiate Test
messages from different LMP Link Verification procedures. In
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RFC 4209 LMP for DWDM Optical Line Systems October 2005
addition to the Test procedure described in [RFC4204], the trace
monitoring function of [RFC4207] may be used for link verification
when the OLS user ports are SONET or SDH.
In a combined LMP and LMP-WDM context, there is an interplay between
the data links being managed by peer node-to-peer node LMP sessions
and peer node-to-OLS LMP sessions. For example, in Figure 2, the
OXC1-OLS1 LMP session manages the data links between OXC1 and OLS1,
and the OXC2-OLS2 LMP session manages the data links between OXC2 and
OLS2. However, the OXC1-OXC2 LMP session manages the data links
between OXC1 and OXC2, which are actually a concatenation of the data
links between OXC1 and OLS1, the DWDM span between OLS1 and OLS2, and
the data links between OXC2 and OLS2. It is these concatenated links
that comprise the TE links that are advertised in the GMPLS TE link
state database.
The implication of this is that when the data links between OXC1 and
OXC2 are being verified, using the LMP link verification procedure,
OLS1 and OLS2 need to make themselves transparent with respect to
these concatenated data links. The coordination of verification of
OXC1-OLS1 and OXC2-OLS2 data links to ensure this transparency is the
responsibility of the peer nodes, OXC1 and OXC2.
It is also necessary for these peer nodes to understand the mappings
between the data links of the peer node - OLS LMP session and the
concatenated data links of the peer node - peer node LMP session.
2.3. Link Summarization
As in [RFC4204], the LinkSummary message is used to synchronize the
Interface_Ids and correlate the properties of the TE link. (Note
that the term "TE link" originated from routing/signaling
applications of LMP, and this concept does not necessarily apply to
an OLS. However, the term is used in this document to remain
consistent with LMP terminology.) The LinkSummary message includes
one or more DATA_LINK objects. The contents of the DATA_LINK object
consist of a series of variable-length data items called Data Link
sub-objects describing the capabilities of the data links.
In this document, several additional Data Link sub-objects are
defined to describe additional link characteristics. The link
characteristics are, in general, those needed by the CSPF to select
the path for a particular LSP. These link characteristics describe
the specified peer node-to-OLS data link, as well as the associated
DWDM span between the two OLSes.
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RFC 4209 LMP for DWDM Optical Line Systems October 2005
The format of the Data Link sub-objects follows the format described
in [RFC4204] and is shown below for readability:
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+---------------//--------------+
| Type | Length | (Sub-object contents) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+---------------//--------------+
Type: 8 bits
The Type indicates the type of contents of the sub-object.
Length: 8 bits
The Length field contains the total length of the sub-object in
bytes, including the Type and Length fields. The Length MUST
be at least 4, and MUST be a multiple of 4.
The following link characteristics are exchanged on a per data link
basis.
2.3.1. Link Group ID
The main purpose of the Link Group ID is to reduce control traffic
during failures that affect many data links. A local ID may be
assigned to a group of data links. This ID can be used to reduce the
control traffic in the event of a failure by enabling a single
ChannelStatus message with the LINK GROUP CHANNEL_STATUS object (see
Section 2.4.1) to be used for a group of data links instead of
individual ChannelStatus messages for each data link. A data link
may be a member of multiple groups. This is achieved by including
multiple Link Group ID sub-objects in the LinkSummary message.
The Link Group ID feature allows Link Groups to be assigned based on
the types of fault correlation and aggregation supported by a given
OLS. From a practical perspective, the Link Group ID is used to map
(or group) data links into "failable entities" known primarily to the
OLS. If one of those failable entities fails, all associated data
links are failed and the peer node is notified with a single message.
For example, an OLS could create a Link Group for each laser in the
OLS. The data links associated with each laser would then each be
assigned the Link Group ID for that laser. If a laser fails, the OLS
would then report a single failure affecting all of the data links
with a Link Group ID of the failed laser. The peer node that
receives the single failure notification then knows which data links
are affected. Similarly, an OLS could create a Link Group ID for a
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RFC 4209 LMP for DWDM Optical Line Systems October 2005
Shared Risk Link Group Value: 32 bits
See [RFC4202]. List as many SRLGs as apply.
2.3.3. Bit Error Rate (BER) Estimate
This object provides an estimate of the BER for the data link.
The Bit Error Rate (BER) is the proportion of bits that have errors
relative to the total number of bits received in a transmission,
usually expressed as ten to a negative power. For example, a
transmission might have a BER of "10 to the minus 13", meaning that,
out of every 10,000,000,000,000 bits transmitted, one bit may be in
error. The BER is an indication of overall signal quality.
The format of the BER Estimate sub-object (Type = 5; Length = 4) is
as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | BER | (Reserved) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Reserved field should be sent as zero and ignored on receipt.
BER: 8 bits
The exponent from the BER representation described above. That
is, if the BER is 10 to the minus X, the BER field is set to X.
2.3.4. Optical Protection
This indicates whether the link is protected by the OLS. This
information can be used as a measure of link capability. It may be
advertised by routing and used by signaling as a selection criterion,
as described in [RFC3471].
The format of the Optical Protection sub-object (Type = 6; Length =
4) is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | (Reserved) | Link Flags|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Reserved field should be sent as zero and ignored on receipt.
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RFC 4209 LMP for DWDM Optical Line Systems October 20052.4. Fault Management
The Fault Management procedure used between a peer and an OLS follows
the procedures described in [RFC4204]; some further extensions are
defined in this section. The information learned from the OLS-peer
fault management procedures may be used to trigger peer-peer LMP
fault management, or may be used to trigger GMPLS signaling/routing
procedures directly.
Fault management consists of three major functions:
1. Fault Detection
2. Fault Localization
3. Fault Notification
The fault detection mechanisms are the responsibility of the
individual nodes and are not specified as part of this protocol.
Fault detection mechanisms may include a Bit Error Rate (BER)
exceeding a threshold, and loss-of-signal (LOS) and SONET/SDH-level
errors. It is the responsibility of the OLS to translate these
failures into (Signal) OK, Signal Failure (SF), or Signal Degrade
(SD), as described in [RFC4204].
That is, an OLS uses the messages defined in the LMP fault
localization procedures (ChannelStatus, ChannelStatusAck,
ChannelStatusRequest, and ChannelStatusResponse messages) to inform
the adjacent peer node of failures it has detected, in order to
initiate the LMP fault localization procedures between peer nodes,
but it does not participate in those procedures.
The OLS may also execute its own fault localization process to allow
it to determine the location of the fault along the DWDM span. For
example, the OLS may be able to pinpoint the fault to a particular
amplifier in a span of thousands of kilometers in length.
To report data link failures and recovery conditions, LMP-WDM uses
the ChannelStatus, ChannelStatusAck, ChannelStatusRequest, and
ChannelStatusResponse messages defined in [RFC4204].
Each data link is identified by an Interface_ID. In addition, a Link
Group ID may be assigned to a group of data links (see Section2.3.1). The Link Group ID may be used to reduce the control traffic
by providing channel status information for a group of data links. A
new LINK GROUP CHANNEL_STATUS object is defined below for this
purpose. This object may be used in place of the CHANNEL_STATUS
objects described in [RFC4204] in the ChannelStatus message.
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RFC 4209 LMP for DWDM Optical Line Systems October 2005
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